¡@¡@Wire bonding has been used in integrated circuit packaging for many years which has been more full-grown than other bonding methods, and gold wire has been the preferred choice. Because of the rising price of gold every year, copper wire has been increasingly used to replace gold wire. ¡@¡@The main focus of this paper is to simulate 3D copper-Al pad thermosonic wire bonding stage by using 3D finite element method. Firstly, the differences between mechanical analysis (the thermal effect was not considered) and thermo-mechanical coupling analysis from both impact stage and ultrasonic vibration stage, respectively, were compared. Secondly, the differences between copper thermosonic wire bonding analysis and gold thermosonic wire bonding analysis were discussed. Finally, the effects of Al pad thickness variation on the copper thermosonic wire bonding analysis were studied. ¡@¡@Results showed that, due to the mechanical properties will be decreased by thermal effects caused from temperature increasing, the obtained effective stress and efective strain of thermo-mechanical coupling analysis were less than the results obtained from mechanical analysis. The pad plastic defomation in copper thermosonic wire bonding is more critical than gold thermosonic wire bonding. Therefore, copper thermosonic wire bonding will lead to serious pad splashing. Also, quantity of the decreasing of pad plastic deformation was limited by increasing the pad thickness.

The primary objectives of this study were: (1) to verify the effectiveness of ECAE to induce equal amounts of strain and grain refinement in bars of different cross-sectional areas, (2) to determine the effectiveness of ECAE in breaking down the as-cast macrostructure in CDA 101 Cu and in producing a homogeneous material containing micron-scale grains upon recrystallization, and (3) to determine a thermomechanical processing (TMP) schedule (from the ones examined) that produces the best microstructure in terms of grain size and uniformity. The effects of extrus ion route, levels of strain and intermediate heat treatment were investigated. To achieve the first objective, bars having square cross-sections of three different sizes, 19 mm, 25 mm and 50 mm, were processed up to eight ECAE passes through routes A, B, C and E. To achieve the second and third objectives, bars were processed up to eight ECAE passes with and without intermediate heat treatments through routes Bc, C, E and F. ECAE processing was carried out in a 90o extrusion die with sliding walls at an extrusion speed of 2.5 mm/s. Recrystallization studies were carried out on the processed material to evaluate the recrystallization behavior and thermal stability of the material. The as-worked and recrystallized materials were characterized by Vickers microhardness, optical microscopy (OM) and transmission electron microscopy (TEM). Results indicate that similar hardness values, sub-grain morphology and recrystallized grain size are generated in the three bars having different cross-sectional sizes processed through ECAE. ECAE is shown to induce uniform strain in all three billet sizes. ECAE is therefore shown to be effective in scale-up to a size of at least 50 mm, with larger billets giving better load efficiency. Results from the later parts of this study indicate that eight extrusion passes via route Bc produces the best microstructure in terms of grain size and microstructural uniformity. The routes can be arranged in the sequence Bc> E, F> C for their ability to produce a uniform recrystallized microstructure with small average grain size. Macroscopic shear bands are sometimes generated during extrusion depending upon the initial grain morphology and texture of the material.

No description available.

The classical continuum theory is not capable of predicting failure without an external crack growth criteria and treats the interface having zero thickness. Alternatively, a nonlocal continuum theory referred to as peridynamic theory eliminates these shortcomings by utilizing formulation that uses displacements, rather than derivatives of displacements, and including material failure in its constitutive relations through the response functions. This study presents a new response function as part of the peridynamic theory to include thermal loading. Furthermore, an efficient numerical algorithm is presented for solution of peridynamic equations. Solution method relies on the discretization of peridynamic equations at collocation points resulting in a set of ordinary differential equations with respect to time. These differential equations are then integrated using explicit methods. In order to improve numerical efficiency of the computations, spatial partitioning is introduced through uniform grids as arrays of linked lists. Furthermore, the domain of interest is divided into subunits each of which is assigned to a specific processor to utilize parallel processing using OpenMP. In order to obtain the static solutions, the adaptive dynamic relaxation method is developed for the solution of peridynamic equations. Furthermore, an approach to couple peridynamic theory and finite element analysis is introduced to take advantage of their salient features. The regions in which failure is expected are modeled using peridynamics while the remaining regions are modeled utilizing finite element method. Finally, the present solution method is utilized for damage prediction of many problems subjected to mechanical, thermal and buckling loads.

The objective of the research presented in this thesis is to validate the parallel-bonded modeling method in the context of coupled thermo-mechanical simulations. The simulation results were compared with analytical and experimental data, in the attempt to assess the usability of this particular modeling method. Previous studies of numerical approaches that related to the thermal fracturing of hard rock had used continuum-based models with constitutive relations. The simulations in the thesis were conducted using Particle Flow Code (PFC) which was chosen for the research because of its several benefits. The code has unique features such as spontaneous damage development without imposed conditions, and emergent properties such as material heterogeneity, and dynamic behavior giving possibility to monitor synthetic seismic events. The basic code has been available since 1995 and research using the code has produced hundreds of publications. The thermal option for the code is a recent addition and lacked verification, validation and applications. The thesis is the answer for that. In the course of the research work new particle clustering and grouping routines were developed and tested. Three modeling studies were conducted varying from laboratory to field scales. The 2D modeling study of the heated cylinder experiment yielded similar results both in fracture-behavioral and acoustic emission (AE) magnitude ranges when compared with the laboratory data. The 3D cubic numerical specimens, created with breakable particle clusters, were heated, and the induced damage was observed by P wave velocity measurements. The results showed trends comparable to the laboratory data: P wave velocity decreases with rising temperatures of up to 250°C and cluster-boundary cracking occurs, comparable to grain-boundary cracking in the heated rock samples. The large 2D tunnel models captured the phenomena observed in-situ displaying the difference in the damage to the roof and floor regions, respectively. This damage was due to the filling material confinement of about 100 kPa on the tunnel floor. In general, the results of the thermo-mechanical simulations were in accordance with the experimental data. The modeled temperature evolutions during the heating and cooling periods were also in accordance with the experimental and analytical data.

Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.

The objective of the research presented in this thesis is to validate the parallel-bonded modeling method in the context of coupled thermo-mechanical simulations. The simulation results were compared with analytical and experimental data, in the attempt to assess the usability of this particular modeling method. Previous studies of numerical approaches that related to the thermal fracturing of hard rock had used continuum-based models with constitutive relations. The simulations in the thesis were conducted using Particle Flow Code (PFC) which was chosen for the research because of its several benefits. The code has unique features such as spontaneous damage development without imposed conditions, and emergent properties such as material heterogeneity, and dynamic behavior giving possibility to monitor synthetic seismic events. The basic code has been available since 1995 and research using the code has produced hundreds of publications. The thermal option for the code is a recent addition and lacked verification, validation and applications. The thesis is the answer for that. In the course of the research work new particle clustering and grouping routines were developed and tested. Three modeling studies were conducted varying from laboratory to field scales. The 2D modeling study of the heated cylinder experiment yielded similar results both in fracture-behavioral and acoustic emission (AE) magnitude ranges when compared with the laboratory data. The 3D cubic numerical specimens, created with breakable particle clusters, were heated, and the induced damage was observed by P wave velocity measurements. The results showed trends comparable to the laboratory data: P wave velocity decreases with rising temperatures of up to 250°C and cluster-boundary cracking occurs, comparable to grain-boundary cracking in the heated rock samples. The large 2D tunnel models captured the phenomena observed in-situ displaying the difference in the damage to the roof and floor regions, respectively. This damage was due to the filling material confinement of about 100 kPa on the tunnel floor. In general, the results of the thermo-mechanical simulations were in accordance with the experimental data. The modeled temperature evolutions during the heating and cooling periods were also in accordance with the experimental and analytical data.

A comprehensive three dimensional coupled thermo-mechanical finite element study is performed on turbine blade attachments in gas turbine engines. The effects of the self-generated centrifugal forces of the disc and the associated blades, thermal loads, and shot peening residual are all considered in this thesis. Three aspects of the work were accordingly examined. The first was concerned with the coupled thermo-mechanical stress analysis and load sharing between the teeth of the fir-tree root. The second was devoted to the development of a complete model incorporating the effect of shot peening residual stresses upon the developed stress state. The effectiveness of shot peening treatment in response to cyclic thermo-mechanical loadings at the contact interface has also been studied. The third was concerned with the validation of some aspects of the developed models analytically using closed form solutions and experimentally using photoelasticity.

A comprehensive three dimensional coupled thermo-mechanical finite element study is performed on turbine blade attachments in gas turbine engines. The effects of the self-generated centrifugal forces of the disc and the associated blades, thermal loads, and shot peening residual are all considered in this thesis. Three aspects of the work were accordingly examined. The first was concerned with the coupled thermo-mechanical stress analysis and load sharing between the teeth of the fir-tree root. The second was devoted to the development of a complete model incorporating the effect of shot peening residual stresses upon the developed stress state. The effectiveness of shot peening treatment in response to cyclic thermo-mechanical loadings at the contact interface has also been studied. The third was concerned with the validation of some aspects of the developed models analytically using closed form solutions and experimentally using photoelasticity.

Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.